Shareholders' Equity - AOCI Components (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Repurchase of shares
Repurchase of common stock (in shares)	0	0
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ (4,101)		$ (204)
Maximum
Repurchase of shares
Number of common shares authorized to be repurchased	4,000,000
Unrealized appreciation (depreciation) on securities
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	$ 24,907		33,051
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	15,905		20,899
Defined benefit pension plan
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(32,387)		(34,112)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	(20,006)		(21,103)
Accumulated Other Comprehensive Loss
Pre-tax amounts:
Accumulated other comprehensive income (loss) before tax	(7,480)		(1,061)
After-tax amounts:
Accumulated other comprehensive income (loss), after tax	$ (4,101)		$ (204)